Friday, March 12, 2010
In 1655 Christian Huygens, back in 1655 discovered Titan, the largest moon of Saturn. Not long after, Giovanni Cassini discovered the next moons, Tethys, Dione and Iapetus. Now you know where the Cassini-Huygens spacecraft got its name. However,John Herschel was the person who actually named Saturn's moons in 1847. Herschel named the seven moons that were known at that time after the Greek Titans. He thought it made sense that the brothers of Cronus (the Roman name for the Greek god Saturn) should be included as the names of the moons. Since that time many other moons have been found hiding amongst the rings of Saturn; They're up into the mid-fifties now.
Titan is the biggest of Saturn's moons and one of the largest moons in the solar system - bigger than the planet Mercury! Its a moon that actually has an atmosphere - a really thick one. This atmosphere is about 98% nitrogen, the only other nitrogen-rich atmosphere in the solar system, and the remaining gases are composed primarily of methane and other hydrocarbons. Titan's atmosphere is a Hadley cell, meaning warm air at the equator rises, flows at high altitudes to the poles, and then descends again, and then moves along the surface. The result of this is extremely dry equatorial regions and "wet" polar regions. Its also extremely cold, around -180 Celsius (-290 degrees Fahrenheit). The mixture of this Hadley cell and the extremely cold temperatures allows methane to rain down in the polar regions.
The evolution of Titan is thought to be different than that of the inner planets or the Jovian moons (which are of a similar size and density), both of which have interiors that have split into distinctive layers.
The Cassini-Huygens spacecraft arrived to study the Saturn system in 2004, and has since made some amazing discoveries. In today's issue of Science, two articles revealed more interesting details about Saturn's largest moon. The Sohl article, on page 1338, revealed details about the moon's interior, also referring to a second study about the Titan's gravitational field. On page 1367 of the issue, Iess et al. presented evidence on the gravitational field of Titan, revealing that the interior of the moon was much colder than previously thought. Why is that important? Well, it informs us about how the internal materials are distributed; this extreme cold impeded the melting and subsequent separations of the primordial ice-rock mixture during moon formation. Only about the first 300 miles deep of Titan's icy surface is rock free, below that you see this ice-rock mixture. This information suggests that Titan more similar to Jupiter's moon Callisto, which is believed to have a similar interior, even though these moons have radically different histories.
Read the story here: http://www.sciencedaily.com/releases/2010/03/100311143830.htm
and the original Science articles here: http://www.sciencemag.org/cgi/content/summary/327/5971/1338
(top image from jpl.nasa.gov)